The three injured persons were brought from Dholkumro village under Kankartala police station in neighbouring Birbhum district to Asansol sub-divisional hospital in an MUV last night.
A woman, wife of one of the injured, the driver of the MUV and his assistant were the three who were detained from the hospital premises, police said.
The injured were identified as Shekh Kalim, Sheikh Mujam and Sheikh Munir.
It is being suspected that they had sustained injuries in an explosion while making bombs at Dholkumro village, police said.